Figure 4. DNA synthesis measured by BrdU incorporation assays. BmMSC from donors 1, 3, 10, 12, and 13 were seeded into 96-well culture plate (1.2 × 102 cells/well). Cells were either left untreated or treated with 4, 8, 12, and 16 mM Na2SO4 (Merck, Darmstadt, Germany) for 48 h. Then, either BrdU or PBS was added in medium, and cells were incubated for 24 h. Subsequently, cells were subjected to detection of the BrdU signals. The fold increase in DNA synthesis was calculated by comparing the BrdU signals of Na2SO4 treated cells to that of untreated cells (to which a value of 1 was assigned). The gender and age of donors are as indicated in the figure. Data represent the mean ± S.D. from three duplicate analyses. **, p<0.05; *, p=0.051 (comparison of individual aged sample to the average of adult samples, t-test).